In a single-wafer rapid thermal processing (RTP) reactor, one of the critical process parameters is the temperature of the wafer. Therefore, it is important to measure the wafer temperature in real-time by a noninvasive and reliable temperature sensing device. Precise, reproducible, noninvasive, and process-independent measurements of the wafer temperature are among the most important requirements of single-wafer optical semiconductor processing tools (such as RTP) in integrated circuit manufacturing.
A typical noncontact temperature measuring device is a single pyrometer which is usually capable of detecting infrared radiation emitted from a heated surface and its subsequent conversion to a temperature. RTP reactors usually comprise a quartz or metallic process chamber inside which the wafer is heated either on both sides by a double bank of heating lamps (tungsten-halogen or arc) surrounding the chamber or only on one side by a single bank of heat lamps. Optical pyrometry has been used as a noninvasive method for wafer temperature measurement in the commercially available RTP systems. However, the accuracy and reproducibility of pyrometry are very sensitive to the wafer surface optical properties (or emissivity), interference by the heating lamps, process environment, and the type of process being performed in the machine. With the double-sided lamp heating arrangement, the pyrometer will usually experience direct radiation exposure from the lamps regardless of the positioning of the pyrometer. However, the disturbance of the pyrometer reading will be minimal if the spectral distribution of the heating photons has no overlap with the pyrometer's operating spectral band or wavelength.
With the single-sided lamp heating arrangement, a hole can be formed through a side of the RTP vacuum chamber opposite the heat lamps in order to insert an optical window, and a pyrometer can be placed near the hole to detect the emitted infrared radiation. This arrangement may be somewhat more suitable than the above-mentioned double heat lamp arrangement since it is free from direct viewing of the lamp and its interference effects. However, a silicon wafer becomes at least partially transparent to the lamp radiation in the infrared region (e.g., ".gtorsim.1.5 microns) at lower temperatures (e.g., in the range of T.ltorsim.600.degree. C.), so the pyrometer may still be affected by lamp radiation passed through a partially transparent wafer. Thus, there is a need for an improved and reliable method and apparatus to precisely measure the temperature of a wafer in a single-wafer RTP reactor.